Method of manufacturing powdered metal plates



Oct. 20, 1953 F. DE MARINIS IIETHOD OF MANUFACTURING POWDERED METAL PLATES Original Filed D60. 28, 1944 Fig.1

INVENTOR F/qnzpemrinis Patented Oct. 20, 1953 METHOD OF MANUFACTURING POWDERED METAL PLATES Frank De Marinis, Cleveland Heights, Ohio, assignor to The S. K. Wellman Company, Cleveland, Ohio, a corporation of Ohio Original application December 28, 1944, Serial No. 570,079. Divided and this application April 21, 1949, Serial No. 88,881

2 Claims. 1

This invention relates to methods of manufacturing powdered metal plates and more particularly to the use of special furnace separator members in such methods.

One of the objects of the invention is the use of a new and improved furnace separator member that under pressure and high temperatures will have a comparatively low thermal coefllcient of expansion, a high creep strength, and that will have a smooth surface that will not bond to powdered metal during sintering operations.

Another object of the invention is the provision of a new and improved furnace separator member that is scale resistant to a large extent under sintering conditions of powdered metal or which, if scales should form, will return the scales rather than release them to the article that is being treated.

A further object of the-invention is the use of a new and improved furnace separator member that leaves the sintered article with a smooth and even surface on the side or sides of the article after the sintering and compressing operation has been completed.

A still further object of the invention is the use of a new and improved furnace separator member that will not be deleteriously affected by gases escaping from the powdered metal during the sintering and pressing operation; that will be capable of withstanding high temperatures without serious changes or deterioration; one in which its physica1 properties will not change under either the reducing or the oxidizing atmospheres of the furnace; and one that will not bond with lead or other ingredients of the mix sweated out when the furnace is allowed inadvertently to attain higher than normal brazing temperatures.

Another object of the invention is the use of a new and improved furnace separator that is normally stable in structure, undergoes a minimum physical or chemical change under pressures and high temperatures and that is relatively inexpensive to construct.

Other and further objects and advantages oi the invention will appear from the following description taken in connection with the accompanying drawings in which Fig. 1 is a perspective view of one of the separator members, with parts broken away;

Fig. 2 is a sectional view of a portion of a heat treating furnace showing in position therein structure used in practicing the new method.

In the manufacture of articles from powdered material the major portion of which is powdered metal a considerable amount of heat and pressure is applied. The temperature must be such as to sinter the entire mass of powdered metal and the pressure such as to produce a solid article by causing the sintered metallic particles to coalesce, fuse or weld. In the production of friction disks the temperatures may be around from 1450" to 1900 F. or even more or sometimes less depending on the quality of the powdered material. It is usually around 1450. The pressures may be from to 250 pounds per square inch or even higher. Here again the type of material must be considered.

In commercial production, the powdered material, including powdered metal, is first subjected to a briquetting operation, 1. e., it is first evenly distributed in a mold and then considerable pressure, say around 11 tons per square inch, is applied to form briquettes or cookies as they are referred to in the art. These cookies are then placed on a metal backing member or in certain instances, the backing member is a core sandwiched between two cookies thus forming a disc assembly unit. This core or backing member is of such material, or its surfaces have been so treated, that the cookie, or cookies, under the proper amount of heat and pressure will become sintered and bonded to the core or backing member forming therewith a unitary structure such as a clutch disk or the like.

On a production basis, it is impractical to treat each article separately so the articles are built up in stacks, as they are called, that is, in vertical columns, which may be easily and readily done where the articles are flat as discs or clutch plates. They are stacked in heat treating presses or furnaces where the outside air is prevented from entering during the operation and heat and pressure simultaneously applied. During the sintering operation the air within the chamber is caused to change from an oxidizing to a reducing atmosphere by the use of charcoal and gas or like material in the furnace as disclosed in United States patent to Wellman, 2,258,431 October '7, 1940.

In order to prevent the bonding of the entire mass of the stacks together during the heat treating operation, separator plates are inserted between the different disk assemblies. These separator plates must be of such material, or the surfaces thereof of such material, or be graphited, or otherwise treated so as to prevent the adjacent cookies from becoming bonded together.

It is common practice to employ separators of steel or like material by first painting the surfaces with a water suspension of graphite for preventthereof. But this requires time and labor and it must be done frequently. The-surface oi the separator after it is thus painted is not smooth and even, thus causing the surface of the work to be more or less uneven and pitted. Furthermore, a separator plate of ferrous material is seriously objectionable because. of the expansion, creep. and warping thereof, thus requiring frequent replacements.

All metallic articles have a thermal coemcient of expansion and in certain metals this is much lower than in others. Under continued application of high temperatures and pressures, these articles become permanently distorted or expanded and are said to creep or grow." This growth increases with the pressure and also increases with the temperature applied in making the articles.

The resistance of the material to this permanent deformation or growth is known or referred to in the art as creep strength." In the manufacture of certain types of articles of powdered material the amount of creep strength of the metallic separators employed is not so material, as where the articles are plane surfaces continuous throughout their extent or the tolerances are large, while in others such as disks having hubs or axial openings where the tolerances are small, the creep strength of theseparators becomes very important for the separators must be of such dimensions as to separate all portions of the cookies of one assembly from those of the adjacent assemblies as otherwise the adjacent assemblies may become bonded together at their non-separated points. A peculiarity of a metal plate separator in the form of an annulus when subjected to high temperatures and pressures is that it tends to become permanently distorted or enlarged radially outwardly during continued use so that its inner as well as its outer diameter is increased. It will thus be seen that unless the annulus has great creep strength, it can be used friction plates, disks, and the like, having friction surfaces made frompowdered material, it

'was discovered that the expansion of the separator causes a corresponding expansion and consequent growth of the cores or backing members to which th cookies are bonded. In other words, the expansion of the separator drags the core along with it. If the expansion of the separators is great the expansion of the cores or backing members will likewise be great and vice versa. This is true irrespective of the type of material of the separator core. It is also immaterial whether or not the separators have been graphited. This peculiar characteristic of the expansion of the separator members causing a correspondent expansion of the cores is not well understood. but a large number of experiments with different materials have demonstrated that it is true.

A peculiar characteristic of growth of cores of friction disk assemblies is that, contrary to expectation, the growth of the cores when sandwiched between separators of unlike material is somewhat below the average of that of the two materials when taken separately. For instance.

.in one case the growth of the core sandwiched between two separators of one material was .0324

0. D. and between separators of another material was .0076" O. D. while sandwichedbetween one of each of these materials .0125", 0. D. much below the average of the two. It is evidently desirable that the furnace separators be of a material that has a minimum thermal coemcient of expansion, as otherwise the growth of the steel cores may be objectionable and require too fre quent replacement of separators or trimming of the cores, or both.

Another serious objection to the expansion of the separator members is that when their diameters increase through continued use it is dimcult fectly satisfactory for commercial use, it must have, at least, the following characteristics to a maximum extent:

1. It must have a high creep strength;

2. It must have a low thermal coefficient of expansion; 1

3. It must not bond to the work;

4. It must have a smooth surface under operating conditions and leave a smooth, unpitted surface on the work when the latter is removed from the furnace.

5. It must have a high scaling temperature, i. e., the surface must be free of scales under brazing temperatures even of mixes composed of materials of high melting point. Or, if scales are formed, they should be more strongly adherent to the surface of the separator than to the surface of the work.

6. The surfaces of the separator must not be seriously affected by th furnace atmosphere ,or by the gases escaping from the sintering material and must have a minimum tendency to bond with lead or other metal sweated out when the furnace is allowed inadvertently to attain higher than normal brazing temperatures.

'7. It must not warp on continuous heating and cooling.

' 8. It must not affect the frictional properties of the sintered friction material.

9. If a plated separator is used the plating must be adherent to the base metal under continued operating conditions.

Numerous materials have certain of these retherein, the chromium probably forms a chromium oxide on the surface of the plate or separator after being heated and this oxide does not adhere to the biscuits in the sintering operation. A large number of experiments indicate that a material that has a high creep strength at the the temperatures and pressures employed does not undergo a phase change during the brazing operation. The experiments also indicated that no commercial steels in the ferritic group have sufficiently high creep strength to be practical.

There are a number of alloys in the austenitic group that have this peculiar property of high creep strength but have a high thermal coefficient of expansion, which is objectionable.

It was found that a nickel-chromium-steel alloy of approximately the following analysis was admirably adapted for this type of use:

' (1) Per cent Cr 25-35 Ni 3-5 as desired. Usually around .1596. The remainder principally ferrous material.

(2) Per cent Cr 11-15 Ni 70-80 Mn maximum 1 Si 0.5 C 0 15 Not all nickel-chromium-steel alloys have a low coemcient of expansion, a high creep strength and a surface to which the briquettes will not bond under sintering conditions. Separators of the material of Number 1 analysis have many advantages over those of Number 2, some of which are as follows:

1. It is easier and faster to set up the work with Number 1 separators.

2. Separators of Number 1 may be heated to higher temperatures than Number 2 without injuriously affecting them.

3. Separators of Number 1 material are stronger and harder than those made of Number 2 and therefore do not bend so easily.

4. The use of separators of Number 1 material tions given, varied within wide limits, the powdered material used had approximately the following analysis:

(3) Per cent Cu Sn 4-10 Fe 5-10 Si 2-7 Graphite 3-10 Referring now to the drawings, the reference character I. designates a separator plate which in the form selected to illustrate one embodiment units.

s of the invention comprises a disk-like member having an axial opening I! therethrough. The thickness of the disk may vary considerably, but in the form shown is as indicated above approximately .025" and about 12.875" 0. D. and around 10.5" I. D. The inner and outer diameters of these separators may vary within very wide limits. The material of the disk is substantially that outlined in analysis (2) above.

The furnace is within which the friction disks are heat treated is substantially the same as that shown in Fig. 8 of the patent to Wellman. referred to above, and need not here be described in detail any further than to state that the heating chamber is shown at H and the stack I! of friction disks i8 and separators ID are placed within the protecting air seal structure IS within the furnace beneath the pressure block l9. As shown in Fig. 2 the stack l 5 comprises a series of friction disks assembly units It alternating with the separator plates ID. The friction disks each comprises a steel core 20, Fig. 2, the surfaces of which have been treated by copper plating or the like to cause the cookies to bond thereon and briquettes or cookies of powdered material 2|. and 22 are sintered and bonded on one or both sides of the core to form a disk assembly unit. The separators l0 alternate with these assembly When the stack is in position, the furnace is heated to the proper temperature which is usually aroud 1450 F., sometimes higher, depending on the mix of powdered material and simultaneously a pressure of from to 250 pounds per square inch is applied for causing the sintering of the briquettes and their bonding to the surfaces of the separators.

'Ihe separators being of material that has a low coeilicient of expansion, a high creep strength and a surface to which the briquettes will not adhere, cooperate to prevent, or inhibit, enlargement or growth of the friction disc during the sinterlng operation. This is considered an important feature of the invention. While the thickness and diameters of the separators are given, this is by way of example only, as these dimensions may vary, as desired.

While the method using the type of separators herein disclosed is useful in the bonding of powdered metal onto disks and annular plates for use on brakes and clutches, it is understood that it is intended to be used in the sintering and bonding of powdered metal briquettes or cookies to cores and backing members for forming or manufacturing plates for use in various relations.

It is thought from the foregoing, taken in connection with the accompanying drawing, that the method will be apparent to those skilled in the art and that changes in size, shape, proportions and composition of the material may be made without departing from the scope and spirit of the appended claims.

This application is a division of Serial Number 570,079, filed December 28, 1944, now Patent No. 2,480,076.

I claim as my invention:

1. A method of manufacturing friction plates from metallic cores and briquettes of powdered material which tend to creep when subjected to high temperatures and pressures, which comprises copperizing at least one surface of each of said metallic cores, positioning. briquettes of powdered material, comprising powdered copper and tin as the principal ingredients and silica, carbon, and ferrous material, in contact with 7 said copperized surfaces to form assemblies, arranging said assemblieain stacks alternating with separator members co'mprisinpthin separator plates of an alloy comprising chromium about 11 to 1596, nickel about 70, to aoqtpmanganese about 1%.ma'ximum, silicon about .596, carbon about .1611 and tbe re'mainder principally i'errous materiahsubiecting said stack to a pressure oitrom100t0250 poundspersquare inch ata temperature around 1450', 1'. and simultaneously inhibiting the creep of said cores and causing the bonding of said briquettes to said cores.

2. A method of manufacturing friction plates from metallic cores and briquettes of powdered material which tend to creep when subjected to high temperatures and pressures which comprises conditioning at least one selected surface or each core to promote a bond with said powdered material, positioning briquettes of powdered material, comprising powdered copper and tin as the principal ingredients and silica, carbon, and ferrous material, in contact with said conditioned surfaces to iorm assemblies, arranging said assemblies in stacks alternating with separator members comprising thin separator plates of an alloy comprising chromium about 11 to 15%,

nickel about "10 to 80%. manganese about 1% maximum, silicon abou 5%. carbon about 15% and the remainder principally terrous material. subjecting said stack to a pressure or from 100 w to 250 pounds per square inch at a temperature around 1450' I". and simultaneously inhibiting the creep of said cores and causing the bonding of said briquettes to said cores.

mam: DE mm.

References Cited in the iile of this patent UNITED STATES PATENTS Number Name Date 2,178,527 Wellman Oct. 31, 1939 2,217,802 Koehring Oct. 15, 1940 2,267,372 Calkins at al. Dec. 23, 1941 2,389,061 Kuzmick Nov. l3, 1945 2,480,076 De Marinis Aug. 23. 1949 

2. A METHOD OF MANUFACTURING FRICTION PLATES FROM METALLIC CORES AND BRIQUETTES OF POWDERED MATERIAL WHICH TEND TO CREEP WHEN SUBJECTED TO HIGH TEMPERATURES AND PRESSURES WHICH COMPRISES CONDITIONING AT LEAST ONE SELECTED SURFACE OF EACH CORE TO PROMOTE A BOND WITH SAID POWDERED MATERIAL, POSITIONING BRIQUETTES OF POWEDERED MATERIAL, COMPRISING POWDERED COPPER AND TIN AS THE PRINCIPAL INGREDIENTS AND SILICA, CARBON AND FERROUS MATERIAL, IN CONTACT WITH SAID CONDITIONED SURFACES TO FORM ASSEMBLES, ARRANGING SAID ASSEMBLIES IN STACKS ALTERNATING WITH SEPARATOR MEMBERS COMPRISING THIN SEPARATOR PLATE OF AN ALLOY COMPRISING CHROMIUM ABOUT 11 TO 15% NICKEL ABOUT 70 TO 80%, MANGANESE ABOUT 1% MAXIMUM, SILICON ABOUT .5%, CARBON ABOUT .15% AND THE REMAINDER PRINCIPALLY FERROUS MATERIAL SUBJECTING SAID STACK TO A PRESSURE OF FROM 10 TO 250 POUNDS PER SQUARE INCH AT A TEMPERATURE AROUND 1450* F. AND SIMULTANEOUSLY INHIBITING THE CREEP OF SAID CORES AND CAUSING THE BONDING OF SAID BRIQUETTES TO SAID CORES. 